1. What becomes tame

People: Jews of any age. Non-Jews do not become tame, and there is a dispute about whether and to what extent a non-Jew's dead body is metamme.

Kelim: Wood, clothing, leather, sackcloth, clay, bone, and metal. Heres, clay, has unique rules for how it contracts, transmits, and retains tum’ah. The rabbis added glass to this list, with rules similar to heres.

Foods: before they can receive tum'ah, they must undergo hekhsher le-tum'ah, which is contact with liquid.

In general, only people and animals are sources of tum'ah, as I'll describe next.

2. Levels of tum’ah

There are three main levels of tum’ah, all mide-orayta. They are avi avotha-tum’ah, avha-tum’ah, and veladha-tum’ah; a “fathers’ father,” a “father” and a “child.” There are four levels of veladha-tum’ah: rishon, sheni, shelishi, and revi’i.

When tum'ah transmits from one object to another, it generally drops by one levelin the next object. Lower levels of tum'ah are generally more limited in how and to what they can be metamme.

Here is an outline of what these levels include, mide-orayta:

Avi avotha-tum’ah: a dead body, a grave, or a keli that touched a dead body

Av ha-tum’ah

Original sources

a zav, zavah, niddah, or yoledet, and certain fluids from their bodies

a person or object with tsara’at, and certain fluids from a metsora’s body

a sherets

a nevelah

the waters of parah adummah

semen

Contracted

Someone tame from an avi avotha-tum’ah, and kelim touched by such a person

Seats sat upon by a zav, zavah, niddah, or yoledet

Someone who had intercourse with a zavah, niddah, or yoledet

Velad ha-tum'ah

Rishon: people, kelim, food, or liquid that became tame from an avha-tum’ah; a first-time zav

Sheni: food or liquid that touched a rishonle-tum’ah; a tevul yom

Shelishi: terumah or kodshim that touched a sheni le-tum’ah; a mehussar kapparah

Revi’i: kodshim that touched a shelishi le-tum’ah

Each of these categories has its own details. More categories were added by rabbinic decrees.

Here, now, is an encyclopedic list of all things tame, at every level. It's stolen from the Encyclopedia Talmudit, volume 19, columns 475–478. By my count it’s 118 different categories:

רביעי לטומאה מדברי סופרים

As I mentioned in part 1, there is no issur whatsoever in spreading tum'ah at any of these levels, unless you are a kohen or nazir.

3. Transmitting tum’ah

Different types of teme'im transmit tum’ah in different ways, as described in the first perek of Massekhet Kelim.

Magga: Almost all sources of tum’ah are metamme by direct contact with a tahor object. Note that a keli heres has its unique definition of contact.

Massa: Almost all of the avot hatum’ah also are metamme a person who carries them, even if not directly touched. Furthermore,the person's clothing, and anything else he touches while carrying the av ha-tum'ah, also becomes a rishon le-tum'ah.

Ohel: The avi avotha-tum’ah are further metamme through a “tent,” meaning a shared canopy.

Hesset: A zav, zavah, niddah,yoledet, and possibly a metsora are metamme’im through moving something without touching it.

Midras: A zav, zavah, niddah,yoledet, and metsora are metamme’im through a seat.

Bi'ah la-bayit: Tsara’at that enters a house is metamme everything inside. This has more limited reach than the ohel of a dead body.

Two exceptional avot ha-tum'ah lack all of the above ways of transmission. First is a dead kosher bird, nevelat of tahor, which must be swallowed to be metamme. Second is issuk, participation in one of these the ceremonies: the parah adummah, the se'ir ha-mishtalleah, and the burning of korbanot hattat that aren't eaten.

4. Prohibitions for a tame

A tame person has several prohibitions about staying away from holy places and foods, and the punishments can be as severe as karet.

People with different levels of tum’ah are prohibited from entering different areas of Jerusalem and the Temple Mount, as described in Kelim 1:7–9. A tame cannot bring bikkurim, make aliyyah la-regel, sacrifice a korban pesah, or participate in Temple services.

A tame may not eat terumah, hallah, ma'aser sheni, or kodshim. If these foods become tame they are prohibited for eating, or even for hana'ah.

5. How to become tahor

The process of taharah depends on the severity of the tum'ah.

People who are rishon le-tum'ah purify themselves by going to a mikveh. They become tahor at sunset. Tum'ah de-rabbanan is removed immediately by the mikveh.

Higher levels of tum'ah may require waiting a week or more, sprinkling with special waters in the Temple, and bringing sacrifices.